Piston



Patented Dec. 27, 1938 UNITED STATES PISTON Ray E. Day, Grosse Pointe, Mich., assignor to Motor Research Corporation, Detroit, Mich., a corporation of Michigan Application January 22, 1937, Serial No. 121,857

16 Claims.

This invention relates to pistons for internal combustion engines, an object of the invention being to provide a piston which may be fitted relatively closely within the engine cylinder, the

Aconstruction of the piston, however, being such that the diameter of the skirt bearing faces will be effectively controlled to maintain a more nearly uniform clearance between the thrust bearing faces and the cylinder wall while at the same time permitting yieldability of the skirt under thermal loads and adequate support thereof against mechanical loads.

In accordance with one important aspect-of the invention there is provided a piston having opposed skirt bearing members or slippers preferably separated from each other and the piston head, the skirt members being supported from the bosses or boss carrying supports by gooseneck struts or webs extending from the outer edges of the skirt members to the outer sides of the supports, these webs effecting by toggle action a control of the skirt diameter when the bosses move apart slightly as a result of thermalexpansion of the head. The construction, moreover, is such that when the piston is fitted in the cylinder an increased stiffness is imparted to the lower end of the skirt in order to compensate for the normally greater yieldability of' this part of the piston as compared with the upper end which is supported nearer the bosses and, therefore, normally less yieldable. This is accomplished, by way of example, by making the goose-neck webs wider at the top than at the bottom, although it may also be accomplished in other ways, such as by providing webs of uniform width or cross-section but increasing in wall thickness toward the lower ends thereof.

In accordance with another aspect of the invention there is provided a piston having opposed skirt bearing members, such as slipper sections, which are yieldably supported from the bosses preferably, although not necessarily, by means of webs of the type above described, the skirt sections being tied to the bosses or boss carrying supports by metal bands, preferably having a lower coefficient of thermal expansion than the skirt. The bands may be cast in the piston skirt so that a portion of the skirt may slide freely thereon, there being a smooth curvilinear path formed in the skirt. The bands preferably are anchoredto the boss carrying supports. These bands are in pre-stressed taut condition at nor- A mal temperatures of the piston below operating temperatures, i. e. when the piston is substantially unheated and at approximate room temperatures,

The bands are preferably pre-stressed after casting the piston, but in any case are normally under sufficient tension to hold the skirt sections in toward each other or contracted under compression or compressive stresses with the iiexible webs or other resilient connections between the skirt and bosses also under compression. By virtue of this construction very effective control of the skirt diameter under operating conditions is achieved.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawing forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

Fig. 1 is a side view of a piston embodying the several features of the present invention.

Fig. 2 is a vertical section taken through line 2--2 of Fig. 1 in the direction of the arrows.

Fig. 3 is a vertical section taken through lines 3-3 ofFig. 2 in the direction of the arrows.

Fig. 4 is a horizontal section taken through lines 4 4 of Fig. 1 in the direction of the arrows.

Fig. 5 is a view similar to Fig. 4 illustrating one method by which the metal bands may be tightened and pre-stressed in order to hold the skirt sections under compression.

Fig. 6 is an elevational view of the plug or rivet prior to its application to the piston.

Before explaining in .detail the present invention it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawing, since the invention is capable of other embodiments and of being-practicedr or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation, and it is not intended to limit the invention claimed herein beyond the requirements of the prior art.

It will be understood that the drawing is illustrative of present preferred embodiments of the present invention and that various changes in design and arrangement of the parts may be made without departing from the broad scope of the invention. It is contemplated that for certain types of engines the pre-stressed steel bands which tie the skirt sections to the boss carrying extensions or hangers may be omitted, whereas in other types of engines the additional control of the skirt achieved by means of the pre-stressed bands will be found to be highly desirable. Such bands may extend completely around the skirt or thereof a piston, such as herein illustrated, in`

which the steel bands are omitted, the construction otherwise being substantially the same as' herein shown and described, or the equivalent thereof.

The piston shown in the drawing may be cast in one piece in a permanent mold and is preferably, although not necessarily, of. an aluminum alloy. Such an alloy may have a relatively `high coefficient of thermal expansion as compared, for example, to the materials used in the con-v trolV bands. The illustrated piston comprises a cupf-shaped head Ill, the annular sidesr of Vwhich are provided with ring grooves II; Integrally depending from the head at two opposite sides thereof are hangers or extensions I2i into which are cast the Wrist pin bosses I3. These bosses have alined wristy or gudgeon pin openings I4. The bosses are additionally reinforced by means of stiifening Webs or ribs I5 connecting the same to the head and the lower| ends of the hangers I2below the bosses are also ribbed or thickened at I6 to increase the stiffness thereof. The pisf tonl is provided below the head with a bearing skirt which in the present instance takes the form of two opposed arcuate skirt or slipper sections I1 which provide the-entire thrust bearing surfaces for the piston, the outer surfacesfofv the boss carrying extensions I2 being relieved so as `not to engage the cylinder Wall. The skirt sections II are separated from the head by means of slots 50,-andare` also preferably entirelyseparated from'v eachother thereby permitting the same to contract and'expand freely, one with relation to the other.

The skirt or slipper sections II are supportedv from the bossesV or boss carrying extensions I2 by means of pairs of Webs `or struts generally designated by theI numeral I8, a pair of these webs or struts joining each skirt section II to the boss carrying extensions or hangers. Each strut or web I8r is substantially in the form of a gooseneckrhavingreversely extending portions; The struts or. webs I8 of each pair comprise relatively short converging portions I8a extendinginwardly from the opposite outer edges of the skirt section and also comprise widely diverging longer portions or WallsY I8b extending preferably to the outerv sides or faces of the extensions or hangers 'I2,. The web portions I8a and I 8b are joined by an intermediate bowed or curvedl portion I8c. Thus, the skirt sections,Y are supported from the boss extensions I2 by means ofbowed or gooseneck type struts diverging from the outer edges of each skirt section to the bosses. As a result, during operation when the piston head becomes hotter than the, skirt sections, a certain amount of toggle action will be exerted by the` struts or webs t8 upon outward movement of thebosses due to,` thermal expansion of the head, and this toggle action will tend to offsetgoutward expansionv ofthe skirt sections against the cylinder wall. Inother words, the normal tendencyv of theskirt sections to expand against the cylinder wal1,.sometimescausing.A 'seizureA or scoring, is

Vpiston. This construction causes each strut to have greater stiifness at the lower end than at 'the top. Since the top of the skirt is nearer the connection, of, the ,head to the bosses and is nearer Vto thegudgeon or Wrist pin it is normally stiffer. than. the lower end. Hence, by progressively varying the width of the struts this differential` stiffness is compensated for. In the presentembodiment it is also contemplated that the struts or Webs be cast so as to increase in wall thickness toward the lower `ends thereof thereby further compensating for the relative weakness or'greater'flexibility of the lower end of the skirt; as compared to the upper end thereof;

In accordance with a further embodiment of the present invention the skirt or slipper sections II are also tied tothe boss carrying extensions I2v by means of metal bands. These bands may be of suitable metal as, for example, a ferrous alloyl having high tensile strength and are substantially inextensible under the condi-'- tions of use to which the pistonis subjected. In the present instance each skirt section I1 is tied to the members I2V by means ofa'pair of upper and lowerk bands I9 and 20, thel bands being cast so as to extend in part through ribs;

Ila in the skirt. The upper bands I9 may lie just above the upperv edges of'the webs I8 and the lower bands 20 may extend freely through slots in these webs. Each bandemerges from the edges of the skirt sectionon a smooth curve and thence has substantially straight portions I9b spanning the skirt section and the hangers I2. The portions |91)` extend straightinto the hangers I2 and have bent. terminal ends I9a anchoring and locking them in the hangers or extensions I2.

To eliminate Vthe possibility of warping a portion of the skirt by an action similarl to that 50.,

of a bimetallic thermostat under heat, ribs or bosses 5I are formed as a part of the skirt and extend around the upper and lower edges of the bands I9 and 20. The ribs or bosses 5I are of a suiicient size to counteract the tendency of the metal in the skirt to warp due to the difference in the coefficients of thermal expansion' between the skirt and the bands.

After the piston has been cast with the bands I9 and 2D incorporated therein, these bands may be tightened in any suitable manner. As shown, each skirt section I'l has upper and lower holes or apertures 2I opposite the bands and the stiffening ribs IIa of the skirt have recesses or notches 22 therein, thereby exposing a portion of each band at opposite sides the'reof through the medium of the aperture 2I and the recess 22. An anvil 23 having its end adapted to t within the recess 22 and having a wedge shaped recess 24 is positioned as illustrated in Fig. 5. A plug orl rivet 25 (Fig. 6) of soft aluminum or other material is inserted in the aperture 2I and engaged by the end 26 of a tool 21, the rivet being guided inproper position by means of a guide collarA 28 loosely. mounted on the end Vof the tool. If desired a boss may be cast on ythe piston skirt to provide suicient material to hold the rivet 25 in place, the boss being ground and forced inwardly by tool 21 against the band l and also the anvil 23 under sufficient pressure to swage the inner end thereof by causing the metal to flow laterally and produce an upset head 25a overlapping the inner edges of the aperture 2|, thereby securely locking the distorted portion ld of the band and holding it in prestressed condition.

When casting the bands in the skirt sections the bands are preferably coated, except at the terminal anchorage points 19a, with a lubricant material, such as a graphite mixture, to prevent adhesion of the aluminum alloy to the surfaces of the bands and to permit slight compressibility of the coating so that the band will not be clamped by the shrinkage of the aluminum when it cools inthe mold. Since each band extends on a smooth curved path or line through the side edge portions of the skirt section I1 and is relatively free in the skirt, it can be readily tightened so as to draw in the skirt sections. The diierential expansion of the skirt and bands is permitted by the relative sliding of the skirt and the bands. It is probable that the action is for vthe skirt to slide on the band as a guide member since the crimping of the band tends to lock the band and skirt together at the point of crimping of the band.

In accordance with the illustrated arrangement each skirt or slipper section is independent of the other, this by reason of the fact that a pair of bands I9 independently tie each skirt section to the bosses. Although not essential, this method of independently tying each section to the bosses by pre-stressed bands is preferred since it aiords somewhat better control of the skirt sections and prevents the release of the entire skirt if a single band should break.

I claim:

1. A piston comprising a head having depending boss carrying extensions, opposed skirt sections separated from the head, a pair of yieldable webs or struts connecting each skirt section to the extensions, the webs of each pair being substantially of goose-neck formation having relatively short converging portions extending inwardly trom the outer edges of the skirt section and Widely diverging longer portions extending to the boss carrying extensions, said converging and diverging portions being joined by intermediate bowed portions, the cross-section of the skirt section and webs varying from top to bottom thereby imparting increased stiiness to the lower end of the skirt section against mechanical loads during operation.

2. A piston as defined in claim l in which the lower ends of said webs are stiier than the upper ends.

3. A piston as defined in claim 1 in which the webs decrease in width from the upper end toward the lower end thereof.

4. A piston as defined in claim 1 in which the walls of the websare thicker and therefore stiier at or near the lower ends thereof than the upper ends.

5. A piston comprising a head, boss carrying extensions depending from said headya pair of skirt sections at opposite sides of the piston, means for connecting the skirt sections to the head in such a manner that they are resiliently movable in towards each other, and a relatively inextensible band or bands holding a skirt section in toward the other under compressive stress and being pre-stressed under tension at tem'- peratures less than operating temperatures of the piston.

6. A piston comprising a head, boss carrying extensions depending from said head, a pair of skirt sections at opposite sides of the piston, means for connecting the skirt sections to the head in such a manner that they are resiliently movable in towards each other, and a relatively inextensible band or bands holding a skirt section in toward the other under compressive stress and being pre-stressed under tension at temperatures less than operating temperatures of the piston, said band or bands being anchored to said boss carrying extensions.

7. A piston as defined in claim 5 in which each band is distorted to pre-stress the same and held in pre-stressed condition by a headed plug element anchored in the skirt section.

8. A piston as defined in claim 6 in which said headed plug element extends through an aperture in the skirt section and is headed over at the inner face thereof.

9. A piston as dened in claim 5 in which said band extends transversely along the inner wall of the skirt section to permit relative sliding in a curvilinear path between said bands and said skirt section.

10. A piston as defined in claim 1 in which 'each skirt section is independently tied to the boss carrying extensions by means of a relatively inextensible band or bands, each band being anchored in the boss carrying extensions, extending transversely from one edge to the other of the skirt section, and slidingly mounted thereon.

11. A piston as defined in claim 1 in which each skirt section is independently tied to the boss carrying extensions by means of a metal band or bands anchored at opposite ends to the boss carrying extensions and pre-stressed and held taut under tension through the medium of means carried by the skirt section.

12; A piston as dened in claim 5 in which each band is pre-stressed and held taut by means carried by the skirt section.

13. A piston as dened in claim 5 in which each skirt sectionl is held in toward the other under compression by means of a pair of bands each pre-stressed at a point on the skirt.

14. A piston as dened in claim 5 in which said band or bands are formed of metal having a lower coeiiicient of thermal expansion than the metal of the piston.

15. A piston comprising a head, boss carrying extensions depending from said head, a pair of skirt sections at opposite sides of the piston, means for connecting the skirt sections to the head in such a manner that they are resiliently movable in towards each other, a relatively inextensible band or bands holding a skirt section in toward the other under compressive stress and being pre-stressed under tension at temperatures less than operating temperatures of the piston, said bands extending through a portion 4- man each pre-stressed at a point on the skirt, said means comprising ribs formed in the skirts adjacent said bands, said ribs extending over the edges of said bands to provide a suicient body of the metal vof said skirts to modify the lai-metallic thermal action thereof.

RAY E. DAY. 

